Here is a good introduction to the electromagnetic spectrum:
imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html
For a broad overview of ionizing radiation, this link to a World Health Organization site should be helpful:
http://www.who.int/ionizing_radiation/about/what_is_ir/en/index.html
For a sense of just how small atomic particles are, see this animated video:
www.ted.com/talks/just_how_small_is_an_atom.html
For a detailed account of the Goiânia accident, the report of the International
Atomic Energy Agency can be found at:
http://www-pub.iaea.org/mtcd/publications/pdf/pub815_web.pdf
A summary of the event with translations from stories in local Portuguese
language newspapers is here:
http://en.wikipedia.org/wiki/Goiania
The medical paper written by Bob and his colleagues is at:
“Use of Recombinant Granulocyte-Macrophage Colony Stimulating Factor in the Brazil Radiation Accident,” The Lancet, August 27, 1988. An abstract can be found at:
http://www.ncbi.nlm.nih.gov/pubmed/2900402
To calculate your annual dose of radiation, go to:
http://www.epa.gov/radiation/understand/calculate.html